1. Field of the Invention
The present invention relates to a channel equalizer, and more particularly, to a channel equalizer interacting with a Trellis decoder.
2. Description of the Prior Art
FIG. 1 is an example of a conventional channel equalizer for a general single-carrier receiver, illustrating a schematic block diagram for a channel equalizer having a decision feedback equalizer (DFE).
The DFE-structured channel equalizer has a feed-forward (FF) unit 10, a feedback (FB) unit 30, an adder 50, a level decision unit 70, and an error calculation unit 90.
The FF unit 10 eliminates the pre-ghost influence for each symbol of an input signal and the FB unit 30 eliminates the post-ghost influence for each symbol of an input signal. The adder 50 adds a pre-ghost-free value of the FF unit 10 and a post-ghost-free value of the FB unit 30.
The level decision unit 70 determines an output signal having a level, of a plurality of preset levels, nearest to the value obtained at the adder 50. The level decision unit 70 feeds back the level-determined signal to the FB unit 30. The level decision unit 70 determines a preset level for an output signal corresponding to a set signal level, for example, 4-level, 8-level, 16-level, or the like.
The error calculation unit 90 calculates an equalization error value based on a signal output from the adder 50 and a signal output from the level decision unit 70. The calculated equalization error value is output to the FF unit 10 and the FB unit 30. The FF unit 10 and the FB unit 30 each update filter tap coefficients based on the inputted equalization error value.
This conventional DFE-structured channel equalizer has an advantage of having a fast convergence speed with relatively less taps. However, the accuracy of an estimation signal output to the FB unit 30, e.g., a feedback filter, greatly affects the equalization performance of a channel equalizer. Thus, a problem with this conventional DFE-structured channel equalizer is that if an incorrect estimation signal is input to the FB unit 30 from the level decision unit 70, e.g., due to noise, an error propagation phenomenon may occur, which will degrade the equalization performance of the channel equalizer.